Quarter Mile Calculator: Estimate ET and Trap Speed
This tool estimates quarter mile elapsed time (ET) and trap speed from vehicle weight and power, or works backwards to estimate power from a known ET or trap speed. Treat every figure as a rough range.
Quarter mile ET and trap speed
Rough estimates. They ignore traction, gearing, altitude and driver technique.
Weight with the driver on board.
Engine output at the crank.
Wheel hp is converted to crank using a 15% drivetrain loss.
- ET (Estimate A)
- 12.00 s
- ET (Estimate B)
- 12.96 s
- Trap speed (Estimate A)
- 113.6 mph / 182.8 km/h
- Trap speed (Estimate B)
- 108.7 mph / 174.9 km/h
Presented as a range because the two common rules of thumb differ.
How the estimates work
Two commonly cited rules of thumb are shown side by side. Estimate A (fit to faster, better-hooking cars) uses ET = 5.825 x (weight / power)^(1/3) and trap speed = 234 x (power / weight)^(1/3). Estimate B (more conservative) uses 6.290 and 224, which gives a slower elapsed time and a lower trap speed, closer to an average street car.
These are curve fits based on real cars, not physics. They ignore traction, gearing, tyre choice, altitude, air temperature, launch technique and shift points, so your actual run can be quicker or slower than the estimate.
Power is assumed to be measured at the crank unless you choose wheel horsepower, in which case an assumed 15 percent drivetrain loss is added back before the formula is applied. Mixing up the two bases is one of the most common sources of confusion.
Worked example
Take a 3,500 lb car (including the driver) making 400 hp at the crank. Running the two estimates gives a spread rather than a single answer.
- Weight
- 3,500 lb
- Power
- 400 hp (crank)
- ET, Estimate A
- 12.00 s
- ET, Estimate B
- 12.96 s
- Trap speed, Estimate A
- 113.6 mph
- Trap speed, Estimate B
- 108.7 mph
- Trap speed, Estimate A (metric)
- 182.8 km/h
- Trap speed, Estimate B (metric)
- 174.9 km/h
Frequently asked questions
How accurate are quarter mile calculators?
They are rough guides, not predictions. Expect real results to land somewhere around the estimated range and sometimes outside it entirely, because traction, gearing and driver technique matter as much as power to weight.
Why is my real ET different from the estimate?
The estimates assume a clean launch and ideal conditions. Wheelspin, tall gearing, a hot day, high altitude or a missed shift all cost time. A well set up car on a good surface can also beat the estimate.
What is trap speed?
Trap speed is the average speed the car carries through the timing lights at the end of the quarter mile. It is a useful indicator of the car's power to weight even when the launch or the ET is not perfect.
Does the weight include the driver?
Yes. Use the race weight, which is the car plus the driver plus fluids. Leaving out the driver can make the estimate optimistic by a few tenths of a second.
How does altitude affect ET?
Higher altitude means lower air density and less oxygen, so a naturally aspirated engine makes less power and the car runs slower. The estimates here do not correct for altitude, air temperature or humidity.
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Last updated: October 11, 2026